1. Field of the Invention
This invention broadly relates to a pivot mechanism for an electronic sectionalizer which enables the sectionalizer to reliably drop out and away from an upper contact to disable a branch or lateral line from the rest of the power distribution network whenever a fault current is detected by the sectionalizer. More particularly, the present invention concerns a latch and pivot mechanism for drop out of the sectionalizer tube wherein an actuator is positioned between pivot points of a trunnion interconnecting the sectionalizer tube and the lower contacts so that upon firing of the actuator the sectionalizer tube immediately is urged in a downwardly direction away from the upper contact. A spring latch releasably retains the trunnion in a fixed location relative to the tube during normal operation when the branch line protected by the sectionalizer is energized, and the latch is arranged to immediately allow the trunnion to swing as soon as the actuator is fired while the sectionalizer tube begins its downward movement.
2. Description of the Prior Art
High voltage power distribution systems are typically comprised of a main supply line that is connected to a number of branch or lateral lines. Normally, the main line is protected near its source of power by an automatic recloser or a reclosing circuit breaker which is operable to disable the entire system downstream of the recloser if currents above a certain magnitude are detected. Automatic reclosers and reclosing circuit breakers are particularly useful for enabling transient fault currents to clear after which time the recloser can again actuate the circuit; however, if fault current conditions remain, the recloser after one or more attempts to re-energize the circuit will cease operation and cause the distribution system to remain in a de-activated state until attended by a repairman.
In the past, fuse links were often installed at the beginning of each lateral line to protect the line and isolate the same from the rest of the distribution system where over-current conditions existed only in a particular lateral line. Many problems were observed, however, in attempting to coordinate the opening characteristics of the fuse links with reclosing apparatus and to ensure that the fuse link would not melt and open the lateral line before the reclosing apparatus had an opportunity to deactivate the entire system. As a consequence, electronic sectionalizers were developed which instead count the number of times that the recloser opens and closes the circuit. After a specified number of opening and closing cycles or "shots" the electronic sectionalizer disables the lateral line during a subsequent period when the reclosing apparatus has opened if over-current conditions in the lateral line protected by the sectionalizer are detected. For additional disclosure of electronic sectionalizers, reference is hereby made to U.S. Pat. No. 4,553,188 dated Nov. 12, 1985.
Normally, it is desirable for an electronic sectionalizer to be physically interchangeable with conventional electrical cutouts so that the sectionalizer can be easily retrofitted and installed in the mounting structure originally provided to hold the cutout. Consequently, sectionalizers often include an elongated tube assembly that has an upper electrical terminal releasably engageable with the upper contact of the mounting structure, and other type of pivot mechanism that is received on the lower contacts of the mounting structure. The sectionalizer typically includes a chemical actuator or some type of striking device that is fired by a logic circuit of the sectionalizer once the latter has determined that over-current conditions still exist in the lateral line protected by the sectionalizer after one or more cycles of operation of the reclosing apparatus.
The pivot mechanism of many sectionalizers, as for example those illustrated in the aforementioned U.S. Pat. No. 4,553,188 cooperates with a latch that is released or opened by the actuator. That is, the actuator, once fired, causes a latch or release lever to swing, and thereafter a spring and/or the forces of gravity are utilized to complete the pivotal movement and ensure that the sectionalizer tube shifts downwardly away from the upper contact to open the lateral line. Thus, the force exerted by the actuator in such devices does not directly impart movement of the tube toward an isolating position, but merely moves a latch so that either a spring or the force of gravity is subsequently operable to urge the tube to fall away from the upper contact.
In other known devices, such as is illustrated in U.S. Pat. No. 4,636,764, a pivot mechanism in the form of an over-center toggle arrangement is provided which causes the sectionalizer tube to be held in an over-center position when loaded in its normal, current carrying orientation. A toggle lever pivotally connected to the sectionalizer tube moves the same over-center once an actuator carried by the lever is activated. However, much of the force of the actuator is directed toward overcoming the spring-loaded upper contact of the mounting structure which normally biases the tube toward its loaded, over-center orientation. As a consequence, once the actuator is fired to shift the tube over-center, the actuator has relatively little available energy remaining, thereby reducing the likelihood that the lever has sufficient momentum to continue to swing and cause the tube to drop away from the upper contact.
As can be appreciated, sectionalizers which are installed on cut-out mountings are typically exposed to adverse environmental conditions and normally the pivot mechanism is held in a stationary position for extended periods of time. Thus, the pivotal joints of the mechanism are subject to corrosion and ice which may prevent successful drop-out of the sectionalizer tube. Therefore, there is a need for a latch and pivot sectionalizer mounting structure which reliably enables the sectionalizer tube to shift away from the contacts and thereby open the circuit whenever the actuator is activated.